Polyreactive Autoantibodies To explore the mechanism(s) that operate polyreactivity, the intravascular survival and biodistribution of polyreactive antibodies, we performed in vitro alnd in vivo studies with a number of randomly-selected human monoclonal antibodies produced in our Laboratory. We found that the carbohydrate moieties of immunoglobulins are not associated with the multiple binding characteristic of the antibodies. We have shown for the first time that the half-life of polyreactive antibodies is significantly shorter compared to monoreactive counterparts. The short circulatory survival of polyreactive antibodies is an intrinsic property of the molecules associated with the multiple binding. Liver seems to be the major site for the removal of these antibodies from the circulation, perhaps in the form of immune complexes. We also have shown that purified neutrophils bind to polyreactive antibody in a dose-dependent manner. These antibodies, via binding to phagocytic cells could, therefore, facilitate the clearance of a variety of molecules released during cellular injury. Previous work in LOM has shown that CD5 antigen-bearing B cells segregated with B cells producing polyreactive antibodies. To understand the relationship between the expression of the CD5 gene and the production of polyreactive antibodies, we tried to clone the genomic form of the human and mouse gene. We isolated a 17 Kb human clone containing the 3' region of the gene. Attempts are currently made to isolate the 5' region and the regulatory elements of the gene. Furthermore, we isolated a 10 Kb clone from a mouse spleen genomic DNA library. This clone contains most of the CD5 gene including the whole first exon and the intramembranous sequences. Mutated constructs of this clone will be used for gene knock-out studies. CR2 Transgenic Mice. Several lines of transgenic mice which express the human CR2 (hCR2) gene at RNA and protein level have been developed. Low but significant binding of anti-CR2 antibodies and biotinylated EBV has been observed. Studies in progress will determine the ability of EBV to infect mouse cells expressing hCR2.